1. Field of the Invention
The invention relates to a method of measuring the defect density of a single crystal and, more particularly, to a method of measuring the defect density of a single crystal for each type of defect.
2. Description of the Related Art
A lattice defect of a semiconductor substrate or an epitaxial film on the semiconductor substrate influences the characteristic of an electronic device, such as a semiconductor device. Thus, the type and density of the defect are extremely important indices in terms of evaluation of quality of the substrate.
Various methods of measuring the defect density of a single crystal are described in the following documents.
Japanese Patent Application Publication No. 2007-318031 (JP-A-2007-318031) suggests that light (photoluminescence light, electroluminescence light, or the like) is irradiated to the inspection surface of an SiC substrate or epitaxial film to map the types and densities of lattice defects (dislocations such as edge dislocations, screw dislocations and basal plane dislocations (edge and screw), and stacking faults) present over the entire inspection surface. JP-A-2007-318031 describes that the types of lattice defects are determined through image analysis of the shapes of defects; however, it does not specifically describe on the basis of what image analysis criteria the acquired optical information is analyzed to determine the types of defects.
Japanese Patent Application Publication No. 2008-28178 (JP-A-2008-28178) suggests a substrate evaluation method that uses both alkali etching and anisotropic dry etching to detect the surface and internal dislocations of a substrate. Japanese Patent Application Publication No. 2001-66122 (JP-A-2001-66122) suggests a method that irradiates white light from a white light source to a measurement target surface and a reference surface while varying a relative distance between these two surfaces to change interference fringes to thereby measure the shape of the measurement target surface. Japanese Patent Application Publication No. 2001-68519 (JP-A-2001-68519) describes a method that separates an enlarged full-color image of an etched crystal face color by color to generate RGB (red, green and blue) color-separated images and then compares the color density of each pixel of each color-separated image with a reference color density to measure the density of etch pits (lattice defects). Japanese Patent Application Publication No. 2006-147848 (JP-A-2006-147848) describes that two-dimensional distribution evaluation of lattice structural defects of a semiconductor sample is conducted by a photoluminescence method in a nondestructive and noncontact manner. Japanese Patent Application Publication No. 8-8315 (JP-A-8-8315) describes a distribution map that is obtained in such a manner that a crystal face is divided by unit area into multiple sections and then the number of crystal dislocations in each unit area is counted.
However, none of the documents clearly describe a method of measuring the defect density for each type of defect.
In addition, Japanese Patent Application Publication No. 1-138449 (JP-A-1-138449) describes a method that converts an X-ray analysis intensity into the number of defects. Japanese Patent Publication No. 3-3946 describes a method that uses a photoacoustic spectroscopy device to measure an acoustic wave generated by expanding and contracting gas in contact with a sample using intermittently irradiated light. Japanese Patent Application Publication No. 9-21756 (JP-A-9-21756) describes a method that detects scattered light reflected on a semiconductor wafer surface layer to which a laser beam is irradiated and then detects surface layer defects from the scattered light image. Japanese Patent Application Publication No. 2001-272340 (JP-A-2001-272340) describes a method of measuring scattered light using data processing based on Rayleigh scattering.
However, none of the methods described in the above documents do not directly observe defects. Therefore, even when the number of defects may be read, it is difficult to separate defects type by type and count the defects for each type.
Furthermore, Japanese Patent Application Publication No. 9-199560 describes a method that measures the densities of various surface defects from an optical microscope image. However, the optical microscope image is two-dimensional information, so it is difficult to distinguish between foreign object and a defect.
Previously, a defect type has been determined through visual judgment within the field of vision of an optical microscope. The accuracy of this determination is at practical level; however, it costs too much work and time to conduct such judgment over a large area, such as a semiconductor wafer, so it is not practical.
Therefore, there is a need for a method of measuring defect densities, which is able to mechanically and accurately determine a defect type.